Graphite lumps or graphite-metallic powder mixed lumps have heretofore been used as brushes. These graphitic brushes, however, are brittle and furthermore, with recent advances in electric motors and so forth, materials which allow a large quantity of electricity to pass therethrough have been required. Under such circumstances, brushes using carbon fibers have been proposed.
Since carbon fibers are electrically conductive and flexible, brushes prepared using such carbon fibers are superior in their ability to conduct electricity and their sliding properties, etc., to conventional brushes made of graphite lumps. By coating carbon fibers with a metal, the ability to conduct electricity therethrough can be further increased. Such brushes are disclosed, for example, in U.S. Pat. No. 3,821,024.
To such brushes there can be provided the ability to conduct electricity by means of multi-point contact by utilizing a design such that one end of each carbon fiber is secured onto a cap (casing) while maintaining its electrical conductivity while the other end is provided in the split fiber state such that it is freely movable. In order to achieve such an arrangement of metal-coated carbon fibers, methods have been employed where one end of the fiber bundle is fixed by an adhesive, or is bound by means of metallic plates, etc., to form a base. These methods, however, give rise to problems, i.e., the ability to conduct electricity is reduced and the carbon fibers are prone to separate or break. Furthermore, the resistance at the joints where the base is connected to the cap and the cap is connected to a wire becomes a problem. Particularly, in connecting the base to the cap, it is necessary to employ techniques such as brazing and welding, because the oxidation of the carbon fibers and reactions between the carbon fibers and the metal should be prevented. In this case, however, severe control is required and mass production is difficult.